液氮冷却作用下高温花岗岩损伤实验

Experimental study on cracking of high temperature granite using liquid nitrogen

关键词:  液氮冷却  花岗岩  低温损伤  热应力

Key words:  liquid nitrogen cooling  granite  low temperature damage  thermal stress

摘要:

液氮作用于高温岩石能够损伤致裂岩石,因此可用于提高干热岩地层的钻井和压裂效率。为研究液氮快速冷却高温岩石对其物理和力学性质的影响规律,分别采用液氮冷却和自然冷却对不同温度(25～600 ℃)的干燥花岗岩岩样进行处理,通过对比两种处理方式下岩样的声波速度、渗透率、抗拉及单轴抗压强度的差异,得到液氮冷却对高温花岗岩的损伤特性。结果表明:液氮冷却可有效损伤高温花岗岩;对于实验中150～600 ℃的花岗岩,经液氮冷却产生的损伤能使其波速降低4.13％～10.04％,渗透率提高0.21～182.80倍,抗拉强度降低4.95％～34.54％,抗压强度降低13.95％～29.30％,弹性模量降低7.33％～45.74％;冷却前岩石温度越高,冷却过程中产生的热应力越大,冷却损伤程度越大。

Abstract:

High temperature rocks can be cracked or damaged when they contact with liquid nitrogen, and thus this method can be used to improve the efficiency of drilling and fracturing in hot dry rock formations. To study the effect of liquid nitrogen cooling on the physical and mechanical properties of hot rocks, air and liquid nitrogen were used to cool dry granite rock samples at different temperature of 25-600 ℃, and the sound velocity, permeability, tensile strength and uniaxial compressive strength of the rock samples were measured and compared. The experimental results show that liquid nitrogen cooling can effectively crack and damage the high temperature granite. The damage to the granite samples under 150-600 ℃ caused by liquid nitrogen cooling can lead the wave velocity decreasing 4.13％-10.04％, the permeability increasing 0.21-182.80 times, the tensile strength decreasing 4.95％-34.54％, the compressive strength decreasing 13.95％-29.30％, and the elastic modulus decreasing 7.33％-45.74％. It is notable that the higher of the temperature of rocks before cooling, the greater thermal stress can be resulted from the cooling process, and the greater degree of cooling damage can be caused.